Process for derivatizing carbon nanotubes with diazonium species and compositions thereof

ABSTRACT

Methods for the chemical modification of carbon nanotubes involve the derivatization of multi- and single-wall carbon nanotubes, including small diameter (ca. 0.7 nm) single-wall carbon nanotubes, with diazonium species. The method allows the chemical attachment of a variety of organic compounds to the side and ends of carbon nanotubes. These chemically modified nanotubes have applications in polymer composite materials, molecular electronic applications, and sensor devices. The methods of derivatization include electrochemical induced reactions, thermally induced reactions, and photochemically induced reactions. Moreover, when modified with suitable chemical groups, the derivatized nanotubes are chemically compatible with a polymer matrix, allowing transfer of the properties of the nanotubes (such as, mechanical strength or electrical conductivity) to the properties of the composite material as a whole. Furthermore, when modified with suitable chemical groups, the groups can be polymerized to form a polymer that includes carbon nanotubes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Divisional application Ser. No.10/632,948 filed Aug. 1, 2003 which sterns from U.S. patent applicationSer. No. 10/470,517, the National Stage Application, filed Jul. 29, 2003of International Application No. PCT/US02/02562, filed Jan. 29, 2002,which application claims priority benefits to U.S. Patent ApplicationSer. Nos. (1) 60/264,784, filed Jan. 29, 2001; (2) 60/272,903, filedMar. 2, 2001; (3) 60/316,501, filed on Aug. 31, 2001; and (4) 60/316,521filed Aug. 31, 2001, all of which are hereby incorporated by reference.

STATEMENT OF FEDERALLY FUNDED RESEARCH

The present invention was made in connection with research pursuant togrant numbers NASA-JSC-NCC 9-77 from the National Aeronautics and SpaceAdministration; grant number NSR-DMR-0073046 from the National ScienceFoundation; and grant number N00014-99-1-0406 from the DARPA/ONR.

BACKGROUND OF THE INVENTION

Fullerenes are closed-cage molecules composed entirely of sp²-hybridizedcarbons, arranged in hexagons and pentagons. Fullerenes (e.g., C₆₀) werefirst identified as closed spheroidal cages produced by condensationfrom vaporized carbon. Fullerene tubes are produced in carbon depositson the cathode in carbon arc methods of producing spheroidal fullerenesfrom vaporized carbon. Ebbesen et al. (Ebbesen I), “Large-ScaleSynthesis Of Carbon Nanotubes,” Nature, Vol. 358, p. 220 (Jul. 16, 1992)and Ebbesen et al., (Ebbesen II), “Carbon Nanotubes,” Annual Review ofMaterials Science, Vol. 24, p. 235 (1994). Such tubes are referred toherein as carbon nanotubes. Many of the carbon nanotubes made by theseprocesses were multi-wall nanotubes, i.e., the carbon nanotubesresembled concentric cylinders. Carbon nanotubes having up to sevenwalls have been described in the prior art. Ebbesen II; Iijima et al.,“Helical Microtubules Of Graphitic Carbon,” Nature, Vol. 354, p. 56(Nov. 7, 1991).

Since 1991, there has been a great deal of interest in derivatization ofcarbon nanotubes, and more, particularly, single-wall carbon nanotubes,to facilitate their manipulation, to enhance the solubility of suchnanotubes, and to make the nanotubes more amenable to compositeformation. This is because single-wall carbon nanotubes are one of themore striking discoveries in the chemistry and materials genre in recentyears. Nanotubes posses tremendous strength, an extreme aspect ratio,and are excellent thermal and electrical conductors. A plethora ofpotential applications for nanotubes have been hypothesized, and someprogress is being made towards commercial applications. Accordingly,chemical modification of single-wall carbon nanotubes, as well asmulti-wall carbon nanotubes, will be necessary for some applications.For instance, such applications may require grafting of moieties to thenanotubes: to allow assembly of modified nanotubes, such as single-wallcarbon nanotubes, onto surfaces for electronics applications; to allowreaction with host matrices in composites; and to allow the presence ofa variety of functional groups bound to the nanotubes, such assingle-wall carbon nanotubes, for sensing applications.

While there have been many reports and review articles on the productionand physical properties of carbon nanotubes, reports on chemicalmanipulation of nanotubes have been slow to emerge. There have beenreports of functionalizing nanotube ends with carboxylic groups (Rao, etal., Chem. Commun., 1996, 1525-1526; Wong, et al., Nature, 1998,394:52-55), and then further manipulation to tether them to goldparticles via thiol linkages (Liu, et al., Science, 1998,280:1253-1256). Haddon and co-workers (Chen, et al., Science, 1998,282:95-98) have reported solvating single-wall carbon nanotubes byadding octadecylamine groups on the ends of the tubes and then addingdichlorocarbenes to the nanotube sidewall, albeit in relatively lowquantities (˜2%).

Success at covalent sidewall derivatization of single-wall carbonnanotubes has been limited in scope, and the reactivity of the sidewallshas been compared to the reactivity of the basal plane of graphite.Aihara, J. J. Phys. Chem. 1994, 98, 9773-9776. A viable route to directsidewall functionalization of single-wall carbon nanotubes has beenfluorination at elevated temperatures, which process was disclosed in aco-pending application commonly assigned to the assignee of theApplication, U.S. patent application Ser. No. 09/810,390, “ChemicalDerivatization Of Single-Wall Carbon Nanotubes To Facilitate SolvationThereof; And Use Of Derivatized Nanotubes To Form Catalyst-ContainingSeed Materials For Use In Making Carbon Fibers,” to Margraves et al.,filed Mar. 16, 2001. These functionalized nanotubes may either bede-fluorinated by treatment with hydrazine or allowed to react withstrong nucleophiles, such as alkyllithium reagents. Although fluorinatednanotubes may well provide access to a variety of functionalizedmaterials, the two-step protocol and functional group intolerance toorganolithium reagents may render such processes incompatible withcertain, ultimate uses of the carbon nanotubes. Other attempts atsidewall modification have been hampered by the presence of significantgraphitic or amorphous carbon contaminants. Chen, Y. et al., J. MaterRes. 1998 13, 2423-2431.

It would thus be desirable to develop a direct approach to high degreesof functionalization of nanotubes that would be accommodating (i.e. aone step approach and one that is compatible with certain, ultimate usesof the nanotubes). Such uses include applications to utilize thetremendous strength, extreme aspect ratios, and excellent thermal andelectrical conductive properties of the nanotubes.

Accordingly, it is an object of this invention to provide a method forderivatizing carbon nanotubes, especially the sidewalls and end-caps ofsingle-wall carbon nanotubes, utilizing chemistries that are direct,accommodating, and compatible with the ultimate uses and applications ofthe nanotubes.

SUMMARY OF THE INVENTION

The invention incorporates new processes for the chemical modificationof carbon nanotubes. Such processes involve the derivatization of multi-and single-wall carbon nanotubes, including small diameter (ca. 0.7 nm)single-wall carbon nanotubes, with diazonium species. The method allowsthe chemical attachment of a variety of organic compounds to the sideand ends of carbon nanotubes. These chemically modified nanotubes haveapplications in polymer composites, molecular electronic applications,and sensor devices. The methods of derivatization includeelectrochemical induced reactions, thermally induced reactions (viain-situ generation of diazonium compounds or via preformed diazoniumcompounds), and photochemically induced reactions. The derivatizationcauses significant changes in the spectroscopic properties of thenanotubes. The estimated degree of functionality is ca. 1 out of every20 to 30 carbons in a nanotube bearing a functionality moiety.

The electrochemical induced processes include procedures utilizing anassembly of nanotubes, such as a piece of “bucky paper” or mat, whichcan be held with a silver paste covered alligator clip and immersed inan acetonitrile solution of a diazonium salt and a supportingelectrolyte salt, while applying a potential (typically a negativepotential) to the assembly of nanotubes. By such a process, a molecularwire (such as an oligo(phenylene ethynylene) molecular wire) and also amolecular electronic device have been covalently attached to a nanotube.This represents the marriage of wire-like nanotubes with molecular wiresand with molecular electronic devices.

Such electrochemical processes can be adapted to apply site-selectivechemical functionalization of nanotubes. Moreover, it allows for thecontrolled attachment of two or more different chemical functionalitiesto different locations on the nanotubes.

The thermally induced processes include procedures in which a dispersionof carbon nanotubes in an organic solvent mixture is treated with aprecursor to a reactive diazonium species. This precursor is thentransformed in-situ to the reactive species, and its thermaldecomposition leads to chemical attachment to the carbon nanotubes. Itis believed that such a process has the advantage of scalability andavoids the necessity of isolating and storing potentially unstablediazonium compounds, i.e., the species that reacts with the carbonnanotubes.

Moreover, the thermal induced processes also include proceduresutilizing pre-formed diazonium species. The reactive species can beprepared beforehand, isolated, and added to the mixture. Additionalvariations include variations in the temperature of the process (ambienttemperature and higher and lower temperatures), ratio of reactants, anda variety of organic solvents.

The photochemical induced processes are similar to the thermal inducedreaction except that a photochemical process (not a thermal process) isutilized to cause the decomposition of the diazonium species that leadsto the chemical attachment of the moieties to the carbon nanotubes.

When modified with suitable chemical groups, the nanotubes arechemically compatible with a polymer matrix, allowing transfer of theproperties of the nanotubes (such as mechanical strength) to theproperties of the composite material as a whole. To achieve this, themodified carbon nanotubes can be thoroughly mixed (physically blended)with the polymeric material, and/or, if desired, allowed to react atambient or elevated temperature. These methods can be utilized to appendfunctionalities to the nanotubes that will further covalently bond tothe host polymer matrix, or directly between two tubes themselves.

There are a multitude of variations in the chemical structure of thepolymer matrix, i.e., polyethylene, various epoxy resins, polypropylene,polycarbonate etc. In general, possible composite materials could bemade with chemically modified nanotubes and thermoplastics, thermosets,elastomers, and others. There is also a host of variations possible inthe chemical groups that can be attached to the nanotubes. The specificgroup will be chosen to enhance compatibility with the particularpolymer matrix desired and, if desired, to cause chemical bonding to thehost material.

Furthermore, when modified with suitable chemical groups, the nanotubescan be used as a generator of polymer growth. I.e., the nanotubes wouldbe derivatized with a functional group that could be an active part of apolymerization process, which would also result in a composite materialin which the carbon nanotubes are chemically involved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of certain aryl diazonium salts used toderivatize single-wall carbon nanotubes.

FIG. 2 shows the scheme utilized to prepare Compounds 9 and 11 asreflected in FIG. 1.

FIG. 3 shows the absorption spectra in dimethylformamide for (A) SWNT-pand (B) SWNT-1.

FIG. 4 shows the absorption spectra in dimethylformamide for (A) SWNT-pand (B) SWNT-8.

FIG. 5 shows the Raman spectra from solid samples, with excitation at782 nm, for (A) SWNT-p and (B) SWNT-1.

FIG. 6 shows the Raman spectra in the radial breathing mode region for(A) SWNT-4 and (B) SWNT-p.

FIG. 7 shows the infrared spectra (attenuated total reflectance) ofderivatized nanotubes for (A) SWNT-4 and (B) SWNT-6.

FIG. 8 shows the thermogravimetric analysis data in argon for SWNT-10.

FIG. 9 shows the Raman spectra for (A) SWNT-p, (B) SWNT-2, and (C)SWNT-2 after TGA.

FIG. 10 shows the high-resolution TEM images for (A) SWNT-p and (B)SWNT-4. The scale bar applies to both images.

FIG. 11 shows electrochemical grafting of an aryl diazonium salt onto acarbon surface.

FIG. 12 shows the reaction sequence for derivatization of single-wallcarbon nanotubes by in-situ generation of the diazonium species, andexamples of functionalized phenyl moieties employed in reactions.

FIG. 13 shows the absorption spectra in dimethylformamide for (A) SWNT-pand (B) 18. The spectra for 16, 17, and 19 are similar, with little orno visible structure. The spectrum of the material from the sequence toproduce 20 was essentially equivalent to that shown for SWNT-p.

FIG. 14 shows the Raman spectra from solid samples, with excitation at782 nm, for (A) SWNT-p and (B) 17. The Raman spectra of 16, 18, and 19are similar, but with differing ratios of the peak intensities. In allthese cases, the relative intensity of the disorder mode is increased.The spectrum of the material from the sequence to produce 20 wasessentially equivalent to that shown for SWNT-p.

FIG. 15 shows the reaction sequence for photochemical derivatization ofa single-wall carbon nanotube.

FIG. 16 shows an example of the portions comprising an epoxy resin.

FIG. 17 shows examples of nanotubes that are chemically modified withgroups compatible with the curing agent portion, and reactive with theepoxy portion of a thermosetting resin.

FIG. 18 shows a schematic depiction of carbon nanotube containingcomposite material where the freehand lines represent the polymer matrixthat is cross-linked by the chemically modified carbon nanotubes,creating a thermosetting composite material.

FIG. 19 shows a depiction of chemically modified carbon nanotubescross-linked via disulfide linkages.

FIG. 20 shows the preparation of nanotubes chemically modified withthiophenol moieties.

FIG. 21 shows the preparation of carbon nanotubes chemically modifiedwith pendant epoxy groups that are compatible with the epoxy portion ofa resin and reactive with the curing agent portion of a thermosettingresin, as reflected in FIG. 16.

FIG. 22 shows an example of a composite material based onpoly(methylmethacrylate) and chemically modified carbon nanotubes, basedon a hydrogen bonding motif (indicated by the dashed lines).

FIG. 23 shows an example of chemically modified nanotubes being used ina polymerization process to grow the polymer from the nanotubes.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Electrochemical Derivatizationof Carbon Nanotubes with Diazonium Species

Aryl diazonium salts are known to react with electron deficient olefins,known as the Meerwein reaction. Obushak M. D., et al., Tett. Lett. 1998,39, 9567-9570. In such solution phase reactions, diazonium saltdecomposition is typically catalyzed by a metal salt such as copper(I)chloride, giving a reactive aryl radical. In some cases, the reaction isbelieved to proceed through an aryl cation. This type of chemistry hasbeen successfully applied to the modification of carbon surfaces viagrafting of electrochemically reduced aryl diazonium salts. Delamar, M.,et al., Carbon 1997, 35, 801-807; Allongue, P., et al., J. Am Chem. Soc.1997, 119, 201-207; Ortiz, B., et al., J. Electro. Chem. 1998, 455,75-81; Saby, C., et al., Langmuir 1997, 13, 6805-6813; Delamar, M, etal., J. Am. Chem. Soc. 1992, 114, 5883-5884. Reduction may give an arylradical that covalently attaches to the carbon surface. This techniquehas been applied to both highly ordered pyrolitic graphite (HOPG) andglassy carbon (GC) electrodes.

Methylene chloride and acetonitrile were distilled from calcium hydride.Dimethylformamide was distilled and stored over molecular sieves.Tetrahydrofuran was distilled from sodium/benzophenone ketyl. All otherreagents were obtained commercially and used without furtherpurification.

Carbon Nanotubes. A method for producing small diameter (ca. 0.7 nm)single-wall carbon nanotubes has been developed by Smalley, et al.Nikolaev, P., et al., Chem. Phys. Lett. 1999, 313, 91-97. This method isdisclosed in a co-pending application commonly assigned to the assigneeof the Application, U.S. patent application Ser. No. 09/830,642“Gas-Phase Nucleation and Growth of Single-Wall Carbon Nanotubes fromHigh Pressure CO,” to Smalley et al., filed Apr. 27, 2001, which isincorporated herein by reference. This material is now commerciallyavailable (Carbon Nanotechnologies Inc., HiPco material). As thediameter of these nanotubes is approximately the same as that of C₆₀,these nanotubes are understood to display enhanced reactivity relativeto the larger diameter tubes typically produced by laser oven methods,since the reactivity of C₆₀ has been attributed in part to curvaturestrain. While the present invention is also pertinent to multi-wallcarbon nanotubes and larger diameter single-wall carbon nanotubes, thesesmall diameter nanotubes were primarily utilized during the examplesdemonstrating the present process. A variety of diazonium salts havebeen used, including those that provide moieties conducive to furtherelaboration after attachment of the nanotubes. Also, an oligo (phenyleneethynylene) molecular device similar to the one that has been shown toexhibit memory and room temperature negative resistance (Chen, J. etal., App. Phys. Lett. 2000, 77, 1224-1226) has been attached to thenanotubes.

The following examples, as well as, the other examples described herein,are presented to further illustrate the invention and, are not to beconstrued as unduly limiting the scope of this invention.

A. Examples Nos. 1-11

For the electrochemical derivatization experiments, a piece of buckypaper, formed by filtration of a suspension, was used as the workingelectrode in a 3-electrode cell and immersed in an acetonitrite solutioncontaining the diazonium salt and an electrolyte. The diazonium saltswere probably reduced to aryl radicals at the surface of the buckypaper, and subsequently become covalently attached to the nanotubes. Theconductivity of single-wall carbon nanotubes has been well documented.In general, aryl diazonium salts are easily prepared under conditionsthat tolerate a variety of functional groups. Consequently, the methoddescribed herein allows functionalization of nanotubes with a widevariety of diazonium salts, including those that provide chemicalhandles for additional elaboration after attachment to nanotubes.

The purified single-wall nanotubes (hereafter, SWNT-p) used in thisinvestigation contained little amorphous or other extraneous carboncontaminants. The purification technique for the nanotubes is discussedin more detail below. The fact the SWNT-p contained little amorphous orother extraneous carbon contaminants is significant, as the presence ofsuch material may have hindered the ability to determine whetherprevious derivatization efforts were successful. (While the lack ofimpurities was an issue in the initial demonstrations respecting theoperability of the reactions, it should be noted that these reactionswill work on raw, impurified multi- and single-wall carbon nanotubes,i.e. the reactions will work even in the absence of a purificationprocess.) In addition, the residual iron content (catalyst from thegas-phase growth technique) was <1 atomic % by electron microprobeanalysis (EMPA) (ca. 0.3 atomic %). The diazonium salts used toderivatize SWNT-p are shown in FIG. 1. Compounds 1-7 and 11 wereprepared from the corresponding aniline derivatives by known methods(Kosynkin, D.; Tour, J. M. Org. Lett. 2000), using nitrosoniumtetrafluoroborate as the diazotization reagent Compound 8 was preparedusing the process reported in Kosynkin, D., et al., Org. Lett. 2001, 3,993-995. Compound 9 and 10 were prepared according to scheme reflectedin FIG. 2. Characterization of these compounds is further discussedbelow. Reaction of these compounds with SWNT-p generated SWNT-x, wherex=1-9 and 11-12, respectively.

The small diameter single-wall carbon nanotubes used in thisinvestigation were produced by a gas-phase catalytic technique, usingcarbon monoxide as the feedstock and iron carbonyl as the catalyst.Nikolaev, P., et al., Chem. Phys. Lett. 1999, 313, 91-97; U.S. patentapplication Ser. No. 09/830,642. (These carbon nanotubes are nowcommercially available; Carbon Nanotechnologies Inc., HiPco material).The raw production material was purified by air oxidation at 150° C. fora period of 12 hours, followed by annealing in argon at 800° C. for 6hours. This material was sonicated in concentrated hydrochloric acid(ca. 30 mg in 60 mL), filtered, washed extensively with water and2-propanol, and dried under vacuum. The purity of these samples wasverified by SEM, TEM, and EMPA.

Bucky Paper. The use of bucky paper as a working electrode for thederivatization raises several unique issues. Electrical contact betweenthe source and the bucky paper during the electrochemical process is anissue. This situation can be improved by application of colloidal silverpaste to the alligator clip used to hold the bucky paper. It is alsobelieved that the success of the reaction is at least partiallydependent on the quality of the bucky paper employed as the workingelectrode. Accordingly, it was helpful to achieve a suspension thatcontained little or no visible particulate prior to filtration to formthe bucky paper.

General procedure for diazotization of aniline derivatives. A portion ofnitrosonium tetrafluoroborate (1.2 molar equivalents) was weighed out ina glove box and sealed. After removal from the glove box, acetonitrilewas added (3 mL/mmol of aniline), and the solution was cooled to −30° C.A solution of the aniline derivative (1 molar equivalent) inacetonitrile (ca. 1 mL/mmol) was added dropwise while stirring (videinfra). In some cases, dry methylene chloride was used as a co-solventfor the aniline derivative. After complete addition, stirring wascontinued for 30 minutes, at which time the cold bath was removed. Afterstirring for a total of 1 hour, the solution was diluted with a 2×volume of ether and stirred. The precipitate was collected by filtrationand washed with ether.

4-Bromobenzenediazonium tetrafluoroborate (1). Yield: 85%. MP 138° C. ¹HNMR (400 MHz, CD₃CN) δ 8.22 (ABq, J=9.1 Hz, Δν=102.1 Hz, 4H).

4-Chlorobenzenediazonium tetrafluoroborate (2). Yield: 78%. MP 134° C.¹H NMR (400 MHz, CD₃CN) δ 8.24 (ABq, J=9.2 Hz, Δν=214.2 Hz, 4H).

4-Fluorobenzenediazonium tetrafluoroborate (3). Yield: 79%. MP 160° C.¹H NMR (400 MHz, CD₃CN) δ 8.64 (dd, J=9.4 Hz, 9.5 Hz, 2H), 7.69 (dd,J=9.4 Hz, 9.5 Hz, 2H).

4-tert-Butylbenzenediazonium tetrafluoroborate (4). The4-tert-butylaniline was dissolved in a 1:1 mixture of acetonitrile anddry methylene chloride prior to addition to the nitrosoniumtetrafluoroborate. Yield: 78%. MP 91° C. IR (KBr) 3364.8, 3107.3,2968.6, 2277.2, 1579.2, 1482.0, 1418.0, 1373.5, 1269.8, 1056.9, 841.1,544.6, 621.4 cm⁻¹. ¹H NMR (400 MHz, CD₃CN) δ 8.16 (ABq, J=9.0 Hz,Δν=298.7 Hz, 4H), 1.30 (s, 12H). ¹³C NMR (100 MHz, CD₃CN) δ 168.85,133.67, 130.43, 111.88, 37.86, 30.84.

4-Nitrobenzenediazonium tetrafluoroborate (5). Yield: 67%. MP 142° C. ¹HNMR (400 MHz, CD₃CN) δ 8.72 (ABq, J=9.4 Hz, Δν=65.4 Hz, 4H).

4-Methoxycarbonylbenzenediazonium tetrafluoroborate (6). Yield 80%; MP113° C. IR (KBr) 3103.8, 3042.4, 2955.3, 2294.7, 2310.1, 1731.4, 1582.9,1439.5, 1306.4, 1045.23, 953.1, 860.9, 758.5, 666.3, 528.0 em⁻¹. ¹H NMR(400 MHz CD₃CN) δ 8.51 (AB₉, J=9.1 Hz, Δν=77.9 Hz, 4H), 3.97 (s, 3H).¹³C NMR (100 MHz, CD₃CN) 165.02, 142.44, 134.12, 133.16, 119.77, 54.43.

4-Tetradecylbenzenediazonium tetrafluoroborate (7). The4-tetradecylaniline was dissolved in a 1:1 mixture of acetonitrile anddry methylene chloride prior to addition to the nitrosoniumtetrafluoroborate. Yield: 69%. MP 82° C. IR (KBr) 3103.8, 2919.5,2289.6, 1577.8, 1473.7, 1070.8, 1024.8, 844.5, 813.8, 716.9, 541.0,510.2 cm⁻¹. IR (KBr) 3103.8, 2919.5, 2289.6, 1577.8, 1473.7, 1070.8,1024.8, 844.5, 813.8, 716.9, 541.0, 510.2 cm⁻¹. ¹H NMR (400 MHz, CDCl₃)δ 8.02 (ABq, J=8.8 Hz, Δν=370.6 Hz, 4H), 2.76 (t, J=7.7 Hz, 2H), 1.61(quin, J=7.8 Hz, 2H), 1.23 (s, 22H), 0.85 (t, J=7.0 Hz, 3H). ¹³C NMR(100 MHz, CDCl₃) δ 159.92, 133.26, 131.94, 110.96, 37.49, 32.34, 30.87,30.12, 30.10, 30.07, 30.04, 29.91, 29.78, 29.75, 29.72, 23.11, 14.55.

2-[2-(2-methoxyethoxy)ethoxy]ethyl p-toluenesulfonate (13). Sodiumhydroxide (3.65 g, 91.3 mmol) and tri(ethylene glycol)monomethyl ether(10.0 g, 60.9 mmol) were dissolved in a mixture of tetrahydrofuran andwater (140 mL, 20 mL, respectively). The solution was cooled in an icebath A solution of toluenesulfonyl chloride (12.76 g, 67.0 mmol) in 20mL of tetrahydrofuran was added slowly. The solution was stirred at 0°C. for 3 hours, then poured into 50 mL of ice water. The mixture wasextracted several times with methylene chloride. The combined organiclayers were washed with dilute HCl, then brine, and dried over magnesiumsulfate. After filtration, the solvent was removed by distillation atreduced pressure to give 16.6 g of the product (86% yield). ¹H NMR (400MHz, CDCl₃) δ 7.50 (ABq, J=7.9 Hz, Δν=179 Hz, 4H), 4.09 (app t, J=4.8Hz, 2H), 3.61 (app t, J=4.9 Hz, 2H), 3.55 to 3.52 (m, 6H), 3.47 to 3.46(m, 2H), 3.30 (s, 31), 2.38 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 145.21,133.28, 130.21, 128.28, 72.20, 71.00, 70.85, 69.69, 68.95, 68.26, 59.31,21.96. IR (neat) 3503.3, 2878.5, 1597.9, 1453.1, 1356.3, 1292.0, 1247.0,1177.2, 1097.5, 1019.0, 924.17, 818.0, 776.9, 664.5 cm⁻¹.

4-{2-[2-(2-methoxyethoxy)ethoxy]ethyl}nitrobenzene (14). A portion of 13(9.0 g, 28.3 mmol) was dissolved in 50 mL of dimethylformamide.Potassium carbonate (11.75 g, 85.0 mmol) and 4-nitrophenol (3.82 g, 27.5mmol) were added. The solution was stirred at 80° C. for 16 hours. Aftercooling to room temperature, the solution was poured into water andextracted three times with methylene chloride. The combined organiclayers were washed with water, then brine, dried over magnesium sulfate,filtered, and the solvent was removed by distillation at reducedpressure. Chromatography (silica, hexane:ethyl acetate, 1:2) wasemployed to isolate the product (5.71 g, 73% yield). IR (neat) 3109.2,3078.2, 2878.5, 1726.3, 1588.1, 1511.2, 1337.1, 1106.7, 1050.3, 932.6,845.5, 753.3, 656.1 cm⁻¹. ¹H NMR (CDCl₃) δ 8.07 (d, J=9.3 Hz, 2H), 6.88(d, J=9.3 Hz, 2H), 4.12 (app t, 2H), 3.79 (app t, 2H), 3.62 (m, 2H),3.58 to 3.53 (m, 4H), 3.44 to 3.42 (m, 2H), 3.26 (s, 3H); ¹³C NMR (100MHz, CDCl₃) δ 164.29, 141.93, 126.24, 114.99, 72.29, 71.29, 71.03,70.98, 69.77, 68.60, 59.44.

4-{2-[2-(2-methoxyethoxy)ethoxy]ethyl}aniline (15). A portion of 14(5.77 g, 20.2 mmol) was dissolved in 40 mL of acidic ethanol, and acatalytic amount of 10% palladium on carbon was added. The mixture washydrogenated on a Parr apparatus (60 psi, 70° C.) for 3 hours. Themixture was then filtered over Celite, washing with ethanol. Solidsodium bicarbonate was added, and the mixture was stirred for 2 hoursand, then filtered. The solvent was removed by distillation at reducedpressure, leaving a brown oil (5.0 g, 98% yield). IR (neat) 3441.82,3349.64, 2893.88, 2238.41, 1634.41, 1516.36, 1449.79, 1234.71, 1101.56,906.97, 722.62 cm⁻¹. ¹H NMR (400 MHz, CDCl₃) δ 6.65 (ABq, J=8.7 Hz,Δν=51.5 Hz, 4H), 4.01 (t, J=5.4 Hz, 2H), 3.77 (t, J=4.6 Hz, 2H), 3.69(app t, J=5.6 Hz, 2H), 3.65 to 3.59 (m, 4H), 3.51 (app t, J=4.9 Hz, 2H),3.34 (s, 3H), 3.0 (brs, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 152.30, 140.58,116.75, 116.24, 72.31, 71.14, 71.02, 70.93, 70.30, 68.49, 59.44.

4-{2-[2-(2-methoxyethoxy)ethoxy]ethyl}benzenediazonium tetrafluoroborate(9). Compound 15 was subjected to the procedure described above fordiazotization. The product was not crystalline, but rather a dark red,sticky material that was difficult to manipulate. The residue was mixedthree times with ether, decanting the solvent. This material wassufficiently pure by ¹H NMR, and was used without further purificationor characterization (2.17 g, 52% yield). ¹H NMR (400, MHz, acetone-d₆) δ8.12 (ABq, J=9.5 Hz, Δν=479.5 Hz, 4H), 4.53 (app t, J=4.5 Hz, 2H), 3.92(t, J=4.4 Hz, 2H), 3.68 to 3.66 (m, 2H), 3.61 to 3.56 (m, 4H), 3.46 (t,J=5.4 Hz, 2H), 3.27 (s, 3H).

Compound 10. To a screw-cap tube with a magnetic stir bar was addedBoc₂O (17.6 g, 80.6 mmol), 4-aminothiophenol (10.0 g, 80.6 mmol),triethylamine (13.5 mL, 96.7 mmol), 150 mL of dichloromethane, andN,N-dimethylaminopyridine (4.92 g, 40.3 mmol). The tube was flushed withnitrogen, and the screw-cap was installed. The solution was stirred atroom temperature for 24 h. The solution was then washed with three 75 mLportions of water, the organic layer was dried over magnesium sulfate,then filtered and concentrated. The residue was chromatographed onsilica using hexanes:ethyl acetate (1.5:1) as the eluant. The productwas isolated as a clear oil that crystallized on standing (16.16 g,94%). mp 83-86° C. IR (KBr) 3454.5, 3376.8, 2978.6, 1711.4, 1630.1,1597.4, 1500.0, 1384.4, 1296.0, 1201.0, 1176.3, 1125.4, 857.2, 825.2,669.8 cm⁻¹. ¹H NMR (200 MHz, CDCl₃) δ 7.32 (d, J=8.6 Hz, 2H), 6.70 (d,J=8.6 Hz, 2H), 3.83 (brs, 1H), 4.54 (s, 9H). ¹³C NMR (50 MHz, CDCl₃)169.72, 148.26, 137.05, 116.33, 115.89, 85.49, 28.63.

Compound 11. To a 500 mL round bottom flask cooled to −20° C. was added6.74 mL of BF₃OEt₂ (171.9 mmol). To this was added a solution of 10 (3.0g, 225.3 mmol) dissolved in 30 mL of THF, over a period of 10 min. Tothis was added a solution of t-butylnitrite (5.59 mL, 103.12 mmol) in 20mL of THF. The solution was stirred and allowed to warm to 0° C. over 40min, at which time 400 mL of cold ether was added. The precipitate wascollected by filtration, to obtain 4.14 g (96%) of the desired product.¹H NMR (400 MHz, CD₃CN) δ 8.52 (d, J=9.1 Hz, 2H), 8.0 (d, J=9.1 Hz, 2H),1.54 (s, 9H).

4-hydroxycarbonylphenyldiazonium tetrafluoroborate (12). This compoundwas prepared according to the general procedure (vide supra). Sulfolanewas used as a co-solvent for the 4-aminobenzoic acid. Yield: 60%. IR(KBr) 3247.9, 3105.3, 2305.5, 1732.6, 1416.1, 1386.5, 1300.1, 1232.8,1093.1, 996.1, 906.9, 872.0, cm⁻¹. ¹H NMR (400 MHz, CD₃CN) δ 8.64 (d,J=9.0 Hz, 2H), 8.44 (d, J=9.0 Hz, 2H).

General procedure for electrochemical derivatization of SWNT-p. Theapparatus used for the electrochemical derivatization experiments was a3-electrode cell, with Ag/AgNO₃ reference electrode and platinum wirecounter electrode. A piece of bucky paper (1-2 mg) served as the workingelectrode. The bucky paper was prepared by filtration of a1,2-dichlorobenzene suspension over a 0.2 μM PTFE (47 mm, Sartorius)membrane. After drying under vacuum, the paper was peeled off themembrane, and a piece was excised for use in the derivatization. Thebucky paper was held with an alligator clip, previously treated withcolloidal silver paste (Ted Pella, Inc.), and immersed in anacetonitrile solution of the diazonium salt (0.5 mM for SWNT-1-SWNT-7and SWNT-9; 0.01 M for SWNT-8) and tetra-n-butylammoniumtetrafluoroborate (0.05 M). Care was taken not to immerse the alligatorclip itself. A potential of −1.0 V was applied for a period of 30 min.Care was taken for the exclusion of light, and nitrogen was bubbledthrough the solution during the experiment. After reaction, the portionof the bucky paper that was not immersed in the solution was excised,and the remainder was soaked in acetonitrile for 24 hours, then washedwith acetonitrile, chloroform, and ethanol. After drying, this materialwas sonicated in acetonitrile for 20 minutes, filtered, and washed againwith acetonitrile, 2-propanol, and chloroform. The reaction productswere dried under vacuum at room temperature prior to characterization.Control experiments without a diazonium salt confirm that suchconditions do not affect the nanotubes, as verified by UV/vis/NIR,Raman, and TGA.

Other salts and parameters. A great variety of aryl diazonium salts formodification can be utilized in the process of the invention.Additionally, parameters such as added potential, the duration of theapplied potential, the solvent, and the supporting electrolyte can bevaried. Furthermore, alkyl, alkenyl and alkynyl additions could be usedfor the process of the invention.

B. Characterization

Scanning electron microscopy (SEM) experiments were performed on aPhillips ESEM XL-30, at an accelerating voltage of 50,000 V. Thisinstrument was equipped with an EDAX detector. Samples for TEM imagingwere drop dried from THF onto a 200 mesh lacey carbon grid on a coppersupport. The accelerating voltage was 100 K.V. Raman spectra werecollected on a Renishaw Ramascope, on solid samples, with excitation at782 nm. UV/Vis/NIR absorption spectra were collected on a ShimadzuUVPC-3101, in double beam mode, with solvent reference. FT-IR spectrawere collected using an attenuated total reflectance (ATR) accessory.TGA data were collected in argon, on a TA Instruments SDT-2960. AFMexperiments were performed in tapping mode on a Digital Multi-mode SPM.Samples for these experiments were dispersed by sonication and spincoated on a freshly cleaved mica substrate. EMPA experiments wereperformed on a Cameca SX-50. The instrument was calibrated, and datawere taken from several different points on each sample. The average ofthese points is reported below. NMR data were collected on a BrukerAvance 400. Chemical shifts are reported in ppm downfield from TMS, andreferenced to solvent. Melting points are not corrected.

Electronic Structure and Optical Properties. The electronic structureand optical properties of single-wall carbon nanotubes have been wellinvestigated. Liang, W. Z., et al., J. Am. Chem. Soc. 2000, 122,11129-11137; Jost, O., et al., App. Phys. Lett. 1999, 75, 2217-2219; Wu,J., et al., App. Phys. Lett. 2000, 77, 2554-2556. The UV/VIS/NIRabsorption spectrum of SWNT-p and SWNT-1 is shown in FIG. 3. Thefeatures (van Hove bands) in the spectrum of SWNT-p are due tosingularities in the density of states (DOS), and, in this spectralregion, are attributed to the band gap transitions in semiconductingnanotubes. The width of these features is due to the overlap of featuresfrom tubes of different diameters and chiral indices. These transitionsare no longer visible for SWNT-1, and the spectrum is essentiallyfeatureless. The absorption spectra of SWNT-2-SWNT-7 and SWNT-1-SWNT-12are similar, with no apparent features. The spectra of SWNT-8 (FIG. 4)and SWNT-9 retained some visible features, but these were significantlyreduced relative to SWNT-p. The loss of structure in the absorptionspectra is indicative of significant electronic perturbation of thenanotubes and disruption of the extended π network. This effect is mostconsistent with covalent functionalization rather than simple adsorptionto nanotube walls or end caps.

Raman Spectroscopy. Raman spectroscopy of single-wall carbon nanotubesis also well developed both theoretically and experimentally. Richter,E., et al., Phys. Rev. Lett. 1997, 79, 2738-2740; Rao, A. M, et al.,Science 1997, 275, 187-191; Li, H. D., et al., App. Phys. Lett. 2000,76, 2053-2055. The Raman spectrum of SWNT-p (FIG. 5A) displays twostrong bands; the radial breathing (ω_(r)˜230 cm⁻¹) and tangential(ω_(t)˜1590 cm⁻¹) modes. The multiple peaks seen in the radial breathingmode are presumably due to the distribution of tube diameters in thesample. The weaker band centered at ca. 1290 cm⁻¹ (ω_(d)) is attributedto disorder or sp³-hybridized carbons in the hexagonal framework of thenanotube walls. The minor band at 850 cm⁻¹ is also characteristic ofthese small diameter nanotubes, although its molecular origin is notcertain. The spectrum of SWNT-1 (FIG. 5B) is quite different. Notably,the relative intensity of the disorder mode is much greater. This is aresult of the introduction of covalently bound moieties to the nanotubeframework, wherein significant amounts of the sp² carbons have beenconverted to sp³-hybridization. The Raman spectra of the otherfunctionalized materials display similar modifications, relative toSWNT-p, but to different degrees. The frequency of the disorder mode andthe relative intensities of the three major bands are shown in Table 1.

TABLE 1 Disorder mode frequency and intensity ratios Of major peaks inRaman Scattering Experiments Compound ω_(d) Int.Ratio(ω_(r):ω_(d):ω_(t))^(a,b) SWNT-p 1291 1.0:0.3:2.7 SWNT-1 12951.0:2.2:3.3 SWNT-2 1294 1.0:2.2:4.0 SWNT-3 1295 1.0:2.0:4.0 SWNT-4 12901.0:1.4:3.7 SWNT-5 1291 1.0:1.4:3.7 SWNT-6 1292 1.0:1.5:3.5 SWNT-7 12931.0:1.3:3.8 SWNT-8 1292 1.0:0.7:3.0 SWNT-9 1293 1.0:0.8:2.5 SWNT-11 12921.0:0.8:2.9 SWNT-12 1291 1.0:1.0:3.4 ^(a)ω_(r) = radial breathing mode,ω_(d) = disorder mode, ω_(t) = tangential mode. ^(b)ω_(r) intensitytaken at 265 cm⁻¹; other intensities taken at maxima.

While there is no significant change in the frequency of the disordermode, the intensity of this mode increased relative to the intensity ofthe other two modes in all cases. The intensity of the tangential modeis also increased relative to the radial breathing mode in most cases,and the overall intensity is lower. In some cases, Raman spectracollected after functionalization revealed changes in the relativeintensities of the peaks within the radial breathing mode region. Forexample, the Raman spectra in this region is shown in FIG. 6 for SWNT-pand SWNT-4.

Infrared Spectroscopy. Infrared spectroscopy (FT-IR, ATR) was also usedto characterize some of the derivatized materials. The spectrum ofSWNT-4 (FIG. 7A) clearly shows significant C—H stretching from thetert-butyl moiety at ca. 2950 cm⁻¹. In the spectrum of SWNT-6 (FIG. 7B),the carbonyl (CO) stretch is apparent at 1731 cm⁻¹ (1723 cm⁻¹ inprecursor diazonium salt), along with minor C—H stretching modes in the2900 cm⁻¹ region.

Electron Microprobe analysis. Electron microprobe analysis (EMPA)experiments revealed 2.7 atomic % chlorine for SWNT-2 (average of fourpoints), and 3.5 atomic % fluorine for SWNT-3 (average of five points).These percentages correspond to estimated stoichiometries of CR_(0.036)for SWNT-2, and CR_(0.05) for SWNT-3, where C is a carbon in thenanotube framework, and R is the functionalizing moiety. Accordingly,approximately one out of every 20-30 carbons in the nanotube bears afunctional moiety.

Thermogravimetric Analysis. In thermogravimetric analysis (TGA) ofSWNT-2 (FIG. 8), a total weight loss of ca. 25%, was observed on heatingto 600° C. under argon. After TGA of SWNT-2, the Raman spectrum isrestored to approximately that of SWNT-p, as seen in FIG. 9. It isbelieved that this restoration indicates removal of the functionalmoieties, leaving the nanotubes intact. The stoichiometry estimated fromthe EMPA data predicts a weight loss of ca. 25% in the case of such aremoval. Thus, these figures are in excellent agreement. The TGA andEMPA data for SWNT-3 are also in good agreement. SWNT-p suffers a ca. 5%weight loss following the same temperature profile. TGA data andestimated stoichiometries for the remaining materials (with theexception of SWNT-8, which was not performed) are shown in Table 2.

TABLE 2 Disorder mode frequency and intensity ratios Observed %Stochiometry Compound weight loss Ratio ^(a) SWNT-p 5 NA SWNT-1 35 1/25SWNT-2 30 1/27 SWNT-3 26 1/20 SWNT-4 27 1/34 SWNT-5 26 1/31 SWNT-6 311/28 SWNT-7 39 1/36 SWNT-8 — — SWNT-9 36 1/40 SWNT-11 28 1/44 SWNT-12 241/32 ^(a) Nanotube carbons bearing a functionalized phenyl moiety. Thesevalues are compensated for weight loss at low temperatures due tosolvent evaporation and degassing (ca. 2-4% in all cases).

Table 2 reflects that the degree of functionality for these compounds isat least about one moiety to fortoy carbon atoms, and typically at leastabout one moiety to thirty carbon atoms. The estimated degree offunctionality is ca. out of every 20 to 30 carbons in the nanotubebearing a functionality moiety.

Scanning and Transmission Electron Microscopy. Due to insufficientresolution, analysis of the reaction products by scanning electronmicroscopy (SEM) did not reveal any visible evidence offunctionalization or significant change from SWNT-p. Transmissionelectron microscopy (TEM) imaging of SWNT-4 revealed significant changesdue to the functionalization. In images of SWNT-p (FIG. 10A), thenanotube walls are essentially clean and uniform, and there is noovercoating of graphitic carbon. Images of SWNT-4 (FIG. 10B) revealedthe presence of bumps on the sidewalls of the tubes, on the order of 2-6Å in dimension. These bumps are seen on almost all individual tubes andon the exterior of ropes, though the resolution is not sufficient todetermine whether they are present on the walls of tubes buried withinthe ropes. These features are a result of functionalization.

Solubility. The solubility of single-wall carbon nanotubes is ofsignificant interest to persons skilled in the art of the invention. Thethree solvents most applicable for the underivatized small-diameternanotubes are dimethylformamide, chloroform, and 1,2-dichlorobenzene.SWNT-4 was the only material found to offer significantly improvedsolubility in organic solvents. SWNT-4 was even found to be somewhatsoluble in tetrahydrofuran (THF), as opposed to a complete lack ofsolubility for SWNT-p in that solvent. After sonication for about 30minutes, the THF solution was found to contain approximately 50 mg L⁻¹of SWNT-4, with no visible particulate. After 36 hours, some visibleparticulate was present, but the solvent was still almost black. Thisdark color was retained for at least several weeks. Solubility indimethylformamide, chloroform, and 1,2-dichlorobenzene was alsoimproved, with suspensions being formed much more rapidly than in thecase of SWNT-p, and higher concentrations being achievable. It isbelieved that this improvement in solubility is probably due to theblocking effect of the bulky tert-butyl group, which could inhibit theclose contact necessary for “roping” of the nanotubes.

SWNT-5 and SWNT-8 were found to be more soluble in dimethylformamide,but solubility in other solvents (tetrahydrofuran, toluene, 2-propanol,carbon disulfide) was not improved. SWNT-9 was prepared in an effort toeffect improved solubility in water and other hydrogen bonding solvents.This functionalization, however, had quite the opposite result. SWNT-9was not dispersible in water or water/0.2%/Triton X. Considerabledifficulty was encountered in suspending SWNT-9 in dimethylformamide.

Robustness. In an effort to assess the robustness of thefunctionalization and preclude simple intercalation or adsorption,SWNT-1 was subjected to a variety of conditions. This material wassonicated for 10 minutes at both ambient temperature and 45° C., in bothchloroform and 1,2-dichlorobenzene, filtered, and re-examinedspectroscopically; no discernable changes were observed. Additionally,SWNT-1 was sonicated in 1,2-dichlorobenzene for 10 minutes to dispersethe tubes, then stirred at 75° C. for 3 hours. After filtration andwashing, no spectroscopic changes were observed.

SWNT-3 was re-examined by EMPA after additional sonication inacetonitrile, followed by filtration and washing. The fluorine contentwas 3.6 atomic %, as compared to 3.5 atomic % (vide supra), and hencewithin experimental limits

C. Derivatization Mechanism

While not intending to be bound by theory, it is believed that thefunctionalization described herein is likely initiated in a mannersimilar to that shown in FIG. 11. The aryl radical that is presumablygenerated on reduction may react with a nanotube, leaving an adjacentradical that may further react or be quenched by a solvent or someimpurity, or oxygen. The propensity of the initial aryl radical todimerize or abstract a hydrogen atom from the solvent is minimized bythe fact that the radical is generated at the surface of the nanotubewhere reaction is desired. It is noted that although the reaction mayproceed through an aryl cation, the mechanism is irrelevant to the finalproduct.

Herein lies one principle advantage of utilizing an electrochemicalprocess, as opposed to a solution phase method in which the diazoniumsalt reduction is catalyzed by copper or some other metal. Since thenanotubes would be present in solution at quite low concentration, thearyl radicals would likely be quenched by some other species.Dimerization of nanotubes in the present case is also unlikely, due tolack of mobility in the solid state.

Thermal Derivatization of Carbon Nanotubes with Diazonium Species

Derivatization with aryl diazonium species is not limited to theelectrochemically induced reaction. That is, both direct treatment ofsingle-wall carbon nanotubes with aryl diazonium tetrafluoroborate saltsin solution, and in-situ generation of the diazonium with an alkylnitrite are effective means of functionalization. In-situ generation ofthe diazonium species has advantages in that this method can avoid thenecessity of isolating and storing potentially unstable or lightsensitive aryl diazonium species. The temperature utilized during thethermal reaction would be at most about 200° C., and typically at mostabout 60° C. In some cases, direct treatment with pre-formed diazoniumsalts is observed to be effective at moderate or even room temperature,and it is expected that reactions could be observed at temperaturesbelow room temperature.

A. Examples Nos. 12-17

The nanotubes used in this investigation were again produced by agas-phase catalytic process developed by Smalley et al., and are nowcommercially available (Carbon Nanotechnologies Inc., HiPco material).The production material was purified by oxidation in wet air at 250° C.for 24 hours, then stirring in concentrated hydrochloric acid at roomtemperature for 24 hours. The resulting material was washed with copiousamounts of water, then 10% aqueous sodium bicarbonate, and finally withadditional water. After drying under vacuum, the material was used forthe functionalization reactions.

The reaction sequence is depicted in FIG. 12. In a typical experiment,˜8 mg of single-wall carbon nanotubes was sonicated for 10 minutes in 10mL of 1,2-dichlorobenzene (ODCB). To this suspension was added asolution of the aniline derivative (2.6 mmol, ca. 4 equiv/mol of carbon)in 5 mL of acetonitrile. After transfer to a septum capped reaction tube(Ace Glass, #8648-03) and bubbling with nitrogen for 10 min, 4.0 mmol ofisoamyl nitrite was quickly added. The septum was removed and replacedwith a Teflon screw-cap, and the suspension was stirred at 60° C. forapproximately 15 hours. Due to the system utilized, considerablepressure was attained in the vessel due to the evolved nitrogen. Thiswas alleviated by partially unscrewing the cap for venting every ˜30 minfor the first 3 hours.

After cooling to ˜45° C., the suspension was diluted with 30 mL ofdimethylformamide (DMF), filtered over a Teflon (0.45 μM) membrane, andwashed extensively with DMF. Repeated sonication in, and further washingwith DMF constituted purification of the material.

B. Characterization

Functionalized nanotube materials 16-19 and 21 displayed significantlyaltered spectroscopic properties, akin to those reported for materialsderivatized via the electrochemical method described above. For example,the UV/vis/NIR absorption spectrum of 18 (FIG. 13) shows an almostcomplete loss of the van Hove singularities. This loss of structure ischaracteristic of the disrupted π-system, and again indicates covalentmodification of the nanotubes. In the Raman spectra reflected in FIG.14, the overall intensity of the scattered light is lower, and therelative intensities of the three main modes are altered.

Relative to the tangential mode at ca. 1590 cm⁻¹, the intensity of theradial breathing mode (ca. 250 cm⁻¹) is decreased, and the intensity ofthe disorder mode (1290 cm⁻¹) is significantly increased. The increasein the relative intensity of the disorder mode can be attributed to anincreased number of sp³-hybridized carbons in the nanotube framework,and can be taken as a crude measure of the degree of functionalization.Additionally, as previously discussed, the functionalized phenylmoieties attached to the nanotubes can be removed by heating in an argonatmosphere, and that thermal gravimetric analysis (TGA) consequentlyprovides a quantitative estimate of the degree of functionalization.Upon heating 16-19 to 600° C. in an argon atmosphere, the observedweight loss values were as follows, with the value previously reportedfor the same materials prepared via the electrochemical technique inparenthesis: 16: 26% (30%), 17: 25% (27%), 18: 26% (31%), 19: 23% (26%)21 (not prepared by the electrochemical technique). Material 20 did notdisplay similar changes in the spectroscopic properties or significantmass loss in TGA, even though this moiety can be successfully attachedby the electrochemical technique. The ester bearing material 18 wassuccessfully prepared, in principle giving access to the carboxylic acidmoiety via hydrolysis.

It is of primary interest to compare the degree of functionalizationachievable by the thermal process to that obtained by theelectrochemical processes of the present invention Experiment Nos. 13-18were performed with a large excess of the aniline derivative, i.e.sufficient to provide the diazonium species in amounts equivalent to theamount of diazonium tetrafluoroborate salts used in the previouslydiscussed reported electrochemical examples. Hence, these Examples Nos.13-18 are comparable in this fashion.

For material 16, straightforward comparison is available throughelectron microprobe analysis. This analysis gave a value of 2.2 atomic %chlorine, relative to 97 atomic % carbon. Similar material prepared bythe electrochemical technique was analyzed to have 2.7 atomic %chlorine, relative to 96 atomic % carbon (vide supra).

The TGA data also give additional insight into the relative efficiencyof the thermal method. For example, the mass loss for 19 corresponds toan estimated 1 in 37 carbons in the nanotubes being functionalized,versus the 1 in 34 ratio achieved by the electrochemical method. It isbelieved that the thermal technique is then comparable in itseffectiveness to the electrochemical method for the equivalent material(SWNT-5). It is believed that optimization of the conditions couldprovide a higher degree of functionalization. The observed efficacy issufficient to significantly alter the properties of the single-wallcarbon nanotubes, and will likely be satisfactory for numerousapplications, such as cross-linked materials and composite formation asdiscussed below.

The thermal reaction of the present invention was found to be nearly asefficacious as the electrochemical process of the present invention,although, in certain respects, this thermal reaction is simpler toexecute and more adaptable for scalability.

It is again noted that the chemical derivatization of nanotubes can alsobe successfully performed using pre-formed diazonium species. Thediazonium species can be prepared beforehand, isolated, and added to themixture. The derivatization can then be induced thermally. Additionalvariations include variations in the temperature of the process (ambienttemperature and higher and lower temperatures), ratio of reactants, anda variety of organic solvents.

Photochemical Derivatization of Carbon Nanotubes with Diazonium Species

Example No. 18

Derivatization with aryl diazonium species can also be inducedphotochemically. A photochemical reaction was performed utilizing4-chlorobenzenediazonium tetrafluoroborate, which is the same diazoniumspecies prepared and utilized in Example No. 2. Thus, a suspension ofSWNT-p in 1,2-dichlorobenzene was created by sonication. To thissuspension was added a portion of the diazonium salt dissolved inminimal acetonitrile. The resulting mixture was stirred while residingwithin the chamber of a photochemical reaction apparatus, with anexcitation wavelength of ca 254 nm (an ultraviolet light source). Thelight source for the photochemically induced reaction may be anywavelength, and typically is an ultraviolet or visible wavelength. Thisreaction is reflected in FIG. 15. The resultant material was similar inall respects to SWNT-2 that was prepared by the electrochemicaltechnique of the present invention.

This experiment further confirmed that reaction of the diazonium saltleads to covalent attachment to the nanotube.

Controlled, Site-Specific Functionalization of Carbon Nanotubes withDiazonium Species

By utilizing the electrochemically induced reaction of the presentinvention, control can be exerted to derivatize the nanotubes atspecific sites. Existing technologies (M. S. Fuhrer, et al., “CrossedNanotube Junctions” Science, 288, 21 Apr. 2000, page 494; Yu Huang, et.al., “Directed Assembly of One-Dimensional Nanostructures intoFunctional Networks” Science, 291, 26 Jan. 2001, page 630; Yi Cui, etal. “Functional Nanoscale Electronics Devices Assembled Using SiliconNanowire Building Blocks” Science, 291, 2 Feb. 2001, p 851) can be usedto prepare a crossbar architecture of nanotubes, wherein one nanotube isfixed to a substrate and a second nanotube is suspended a finitedistance above. Both nanotubes can be individually addressedelectrically. Application of opposite potentials to the two tubes causesthe top tube to deform and essentially come into contact with the lowertube. “Contact” as used herein means both actual physical contact, butalso proximity of the entities within an infinitesimally small distance(referred to as van der Walls contact), in which the entities mayinfluence each other on a molecular and electronic scale.

This deformation results in two features of significance. First, the toptube is physically deformed, leading to a potentially higher chemicalreactivity at the point of deformation, based on current understandingof the effects of curvature strain on reactivity. This feature wouldallow selective functionalization at the junction via theelectrochemical technique of reaction with diazonium salts. Secondly,higher potential is achieved at the point of “cross” between the tubes.

In the present invention, directed functionalization of thecrossed-nanotube junctions can be performed by applying a potential tothe ends of the nanotubes (as is known in the art) in the presence ofα,ω-bis(diazonium) salts or mono-diazonium salts with an interactinggroup at the opposite end would permit functionalization at the crosspoint domain.

Any cross bar array of nanotubes could be functionalized by suchprocesses. For instance, a crossbar architecture of nanotubes will beprepared by fluid flow over a patterned substrate, or by direct tubegrowth between posts, or by some other method. Furthermore, thediazonium salt assembly described here could occur in a diazoniumsolution, with voltages on orthogonal tubes, regardless of the assemblymethod for the tube arrays. Application of potentials to the nanotubesin the presence of diazonium salts would permit functionalization at thecross point domain.

The diazonium species are directed by the potential existing at thejunction to react with the surface of the nanotube, thus placingfunctional molecular devices at the junctions. Site-specificfunctionalization could enable the use of nanotubes in molecularelectronic applications since device functionality is critical at thecross points. The crossed nanotubes therefore provide a method ofdirectly addressing the functionalized molecules, including moleculesthat function as molecular switches, molecular wires, and in othercapacities and uses as is generally known in the art.

Furthermore, this process would allow for attachment of differentmolecules to nanotube cross points, i.e., controlled attachment of twoor more different chemical functionalities to different locations onnanotubes. This would be performed by applying a potential at aspecified set of positions while in a solution of a first diazoniumsalt, then moving to a solution of a second diazonium salt and applyinga potential at other positions, etc. In addition, site specificfunctionalization will allow individual molecules or groups of moleculesto be electrically addressed by metallic contact pads or other contactmeans as are known in the art. Just such a molecule of electronicinterest is incorporated into SWNT-8.

Application of Chemically Modified Carbon Nanotubes in Polymer CompositeMaterials

Polymer and polymer/composite materials are widely used for structuralmaterials and a variety of other applications. The derivatized carbonnanotubes made using the processes disclosed herein can be used incombination with existing polymer matrices to create newpolymer/composite materials. In general, possible composite materialscould be made with chemically modified nanotubes and thermoplastics,thermosets, elastomers, and others. There are a multitude of variationsin the chemical structure of the polymer matrix, i.e. polyethylene,various epoxy resins, polypropylene, polycarbonate etc. There is also ahost of variations possible in the chemical groups that can be attachedto the nanotubes. According, it is possible to select a specific polymerand specific moiety to enhance the properties of the particularpolymer/composite material desired.

Thus, the polymer/composite material will have significantly enhancedproperties, such as, for example, enhanced strength and/or conductivity.And, when modified with suitable chemical groups, the nanotubes will bechemically compatible with the polymer matrix, allowing transfer of theproperties of the nanotubes (especially mechanical strength) to theproperties of the composite material as a whole. Typically, to achievethis, the modified carbon nanotubes can be thoroughly mixed (physicallyblended) with the polymeric material, and allowed to react at ambient orelevated temperature.

Thermosets. It may be desired to form a polymer/composite material inwhich the carbon nanotubes are chemically bound at multiple points tothe polymer (thermosets). For example, this can be done, for example,utilizing an epoxy resin. Epoxy resins are typically composed of twoportions that are mixed in a certain ratio. The resulting mixture thenhardens, or “cures,” over a period of time into an adhesive orstructural material. The two parts are the epoxy portion (labeled “A” inFIG. 16, in this case derived from the reaction of bisphenol-A withepichlorohydrin) and the curing agent (labeled “B” in FIG. 16). Thecuring agent contains chemical groups that react with a repeatedlyoccurring chemical group in the epoxy portion. I.e., the cured orcross-linked resin results from the reaction of A (specifically, theterminal epoxide functionalities) with B (specifically, the terminalamine functionalities). Because both the epoxy portion and the curingagent contain numerous reactive groups, a “cross-linked” material iscreated, with numerous chemical bonds that impart strength to the curedmaterial (labeled “C” in FIG. 16). The result of the reaction is ahighly cross-linked thermoset material.

A wide variety of commercially available epoxy components exist, wherethe chemical structure of both parts A and B can vary greatly. Forexample, curing agents may be based on diamines, polymercaptans, phenolcontaining materials, etc., and may be polymeric. The addition ofchemically modified carbon nanotubes to this type of system will greatlyincrease the strength of the resulting material, due to the strength ofthe nanotubes themselves. The nanotubes can be chemically modified withgroups that are compatible with either the epoxy portion or the curingagent portion. For example, modified nanotubes can be prepared as shownin FIG. 17. (In the figures, the shaded cylinder represents the carbonnanotubes).

Carbon nanotubes thus modified will be thoroughly mixed with either thecuring agent portion or the epoxy portion. The resulting material willthen be thoroughly mixed with the second portion and allowed to react,or cure at either ambient or elevated temperature, depending on theparticular system. The resulting composite material will then becross-linked not only by the curing agent, but also by the modifiedcarbon nanotubes, via, for example, aryl-thioether linkages, as shown inFIG. 18, where the freehand lines schematically represent the polymermatrix.

These types of materials can be prepared using a variety of modifiedcarbon nanotubes, exemplified by the examples in FIG. 17. Thus, thelinkages between the polymer matrix and the nanotubes could be ether,thioether, amine, salt bridge (such as SWNT-11 in an amine containinghost polymer) or other linkages. It is understood that the directchemical bond between the nanotubes and the surrounding polymer matrixwill enable the transference of the strength properties of the nanotubesto the composite material itself. It is also noted that enhancement ofthe material properties by the nanotubes may be caused by factors otherthan such direct chemical bonding; for example, improved dispersion ofthe nanotubes within the polymer matrix, enabled by thefunctionalization, may allow enhancement.

In addition to the chemical bond between the nanotubes and thesurrounding polymer matrix, in the case of thiophenol derivatizednanotubes, there will be a chemical interaction between the nanotubesthemselves. The formation of disulfide linkages between nanotubes, asshown in FIG. 19, will serve to further strengthen the material. Thedisulfide linkages can be further reduced (chemically, for instance) toonce again provide the non-crosslinked tubes. Hence, this is astealth-like crosslinking. In fact, such cross-linked nanotubes willrepresent an enhanced strength material in their own right for someapplications.

Another possibility is modification of carbon nanotubes with chemicalgroups that are compatible with the epoxy portion rather than the curingagent portion, such as, for example, shown in FIG. 21. The materialresulting from the incorporation of nanotubes derivatized in this mannerwould again be a chemically bound, three-dimensional network,cross-linked by both the curing agent and the chemically modifiednanotubes.

Other specific chemical interactions between modified carbon nanotubesand a polymer matrix are also possible. For example, a system based on ahydrogen bonding interaction is shown in FIG. 22. This type ofinteraction would be in an extended three-dimensional network, againimparting the strength of the nanotubes to the composite material.

Utilizing the electrochemical process described in this invention, thederivatized nanotubes reflected in FIG. 20 were prepared. From this,what is believed to be a step of deprotection of the thiol was performedby treatment with trifluoroacetic acid in 1,2-dichlorobenzene (acidhydrolysis). Alternatively, this step could be performed by treatmentwith trifluoroacetic acid in dimethylformamide, or by thermolysis at orabout 175° C. Again, the functionalized nanotubes formed as reflected inFIG. 20 would chemically react with, for example an epoxy resin, withthe free thiol group (SH) acting as a crosslinking agent.

Thermoplastics. In addition to thermosets, derivatized nanotubes can beutilized for thermoplastics. As in the case of thermosets, thederivatized nanotubes may or may not be chemically bound to the polymermatrix. It is understood that a modest degree of chemical attachmentbetween the derivatized nanotubes and the polymer matrix could betolerated, while retaining the thermoplastic properties (specifically,the ability to heat and reform the material without significantdegradation). As noted above, physical blending of the carbon nanotubeswith the polymer can be enhanced by the derivatization process(specifically by making the nanotubes more compatible with, or moresoluble in, the host polymer).

For instance, a polymer/composite material containing pure (andunderivatized) single-wall carbon nanotubes may be desired so that thepolymer would have certain enhanced conductive properties; however, thepure and underivatized carbon nanotubes may not sufficiently disperse inthe polymer. By derivatizing the nanotubes with a particular moiety, thederivatized nanotubes could then be dispersed adequately. Because thederivatization of the nanotube may likely have affected the conductivityof the nanotube (and will thus effect the conductivity of thepolymer/composite), it may be desirable to reverse the derivatizationprocess to remove the functional groups from the nanotubes afterdispersal. In this manner, the conductivity of the material can berecovered. This can be done by any process that reverses thederivatization, such as raising the temperature of the polymer/compositematerial to a temperature at which the functional group disassociates.Typically, this temperature appears to be at least about 250° C.

A. Example Nos. 19-25

Moreover, the thermoplastic may also be formed utilizing the derivatizedcarbon nanotube. The functional groups, while not necessarily chemicallybond to the polymer, would be physical extensions from the tube (likebranches from a tree) that will afford additional strength to thepolymer/composite materials. This enhancement may be due to a rougheningeffect on the nanotube surface, increasing friction and reducing slidingof the polymer matrix along the nanotube length. As is understood in theart, such as an effect would further enable transference of thedesirable nanotube properties to the composite material.

Utilizing processes discussed above the following functionalizedsingle-wall carbon nanotubes where prepared where n=1 in 20 to 1 in 40functional groups per nanotube carbons):

This derivatized material (17) was dispersed in High-Impact-Polystyrene(HIPS) at various concentrations. Tensile strength, tensile modulus, and% strain to failure data of the resulting composite material were thengathered. The results of these examples are reflected in Table 3.

TABLE 3 Tensile Tensile % Strain Material Strength (MPa) Modulus (MPa)to Failure HIPS (pure) 18.1 454.5 56.4 1 wt % 17 32.5 729.3 4.6 3 wt %17 17.8 821.3 2.2 3 wt % pristine* 22.8 560.0 11.0 5 wt % 17 26.3 736.53.9 7 wt % 17 22.0 724.4 3.1 *3 wt. %, unfunctionalized nanotubes(SWNT-p), for direct comparison

On the whole, there is a substantial improvement in the tensileproperties of the polymer/composite materials with the functionalizednanotubes. There is improvement over both the pristine HIPS polymer, andover the composite of HIPS and unfunctionalized nanotubes.

Polymerization. Furthermore, a polymer that includes carbon nanotubescan be formed by derivatizing the carbon nanotubes with a functionalgroup that is capable of polymerizing or initiating a polymerization.Once the functional group is attached, standard polymerizationtechniques can then be employed to grow the polymer from the functionalgroup in situ. I.e., the functional group attached to the nanotube couldbe used as a generator of polymer growth. Such standard polymerizationtechniques could be any of the standard known types, such as radical,cationic, anionic, condensation, ring-opening, methathesis, orring-opening-metathesis (ROMP) polymerizations, when appropriate groupsare bound to the nanotubes. For instance, FIG. 23 reflects an example ofa carbon nanotube that has been derivatized with a functional group4-aminophenyl that is subsequently polymerized with styrene to grow thepolymer from the functional group. Accordingly, the functional groupattached to the nanotube would be a chemically active part of thepolymerization, which would result in a composite material in which thenanotubes are chemically involved.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and methods and in the steps or in the sequence of steps ofthe method described herein without departing from the concept, spiritand scope of the invention. More specifically, it will be apparent thatcertain agents which are both chemically and physiologically related maybe substituted for the agents described herein while the same or similarresults would be achieved. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope and concept of the invention as defined by theappended claims.

1. A process comprising: (a) derivatizing a carbon nanotube with adiazonium specie; and (b) covalently attaching a molecular wire to thederivatized carbon nanotube.
 2. The process of claim 1 furthercomprising connecting a molecular electronic device to the molecularwire.
 3. The process of claim 1, wherein the molecular wire comprises anoligo(phenylene ethynylene) molecular wire.
 4. The process of claim 1,wherein the carbon nanotube is a single-wall carbon nanotube.
 5. Theprocess of claim 4 further comprising connecting a molecular electronicdevice to the molecular wire.
 6. The process of claim 4, wherein themolecular wire comprises an oligo(phenylene ethynylene) molecular wire.7. A process comprising: (a) derivatizing a carbon nanotube with adiazonium specie; and (b) covalently attaching a molecular switch to thederivatized carbon nanotube.
 8. The process of claims 7, wherein thecarbon nanotube is a single-wall carbon nanotube.
 9. A method forderivatizing carbon nanotubes comprising: (a) preparing an assembly,wherein (i) the assembly comprises a first plurality of carbon nanotubesand a second plurality of carbon nanotubes; and (ii) wherein the carbonnanotubes in the first plurality and the carbon nanotubes in the secondplurality can be individually addressed electronically; (b) immersingthe assembly in a diazonium specie; and (c) applying a negativepotential to the assembly to cause the first plurality to essentiallycome in contact with the second plurality; wherein applying saidnegative potential facilitates an electrochemical reaction of theassembly with the diazonium specie so as to derivatize at least one ofthe first plurality and second plurality of nanotubes.
 10. The method ofclaim 9, wherein the diazonium specie comprise molecules that functionin a capacity selected from the group consisting of molecular switchesand molecular wires.
 11. The method of claim 9, wherein theelectrochemical reaction of said diazonium specie occurs at a junctionbetween said first plurality of nanotubes and said second plurality ofnanotubes.